* Astronomy

Title: A Study of the Long-term Spectral Variations of 3C 66A Observed with the Fermi and Kanata Telescopes
Authors: Ryosuke Itoh, Yasushi Fukazawa, James Chiang, Yoshïtaka Hanabata, Masaaki Hayashida, Katsuhiro Hayashi, Tsunefumi Mizuno, Masanori Ohno, Takashi Ohsugi, Jeremy S. Perkins, Silvia Raino, Luis C. Reyes, Hiromitsu Takahashi, Yasuyuki Tanaka, Gino Tosti, Hiroshi Akitaya, Akira Arai, Masaru Kino, Yuki Ikejiri, Koji S. Kawabata, Tomoyuki Komatsu, Kiyoshi Sakimoto, Mahito Sasada, Shuji Sato, Makoto Uemura, Takahiro Ui, Masayuki Yamanaka, Michitoshi Yoshida

3C 66A is an intermediate-frequency-peaked BL Lac object detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope.
We present a study of the long-term variations of this blazar seen over 2 years at GeV energies with Fermi and in the optical (flux and polarisation) and near infrared with the Kanata telescope.
In 2008, the first year of the study, we find a correlation between the gamma-ray flux and the measurements taken with the Kanata telescope.
This is in contrast to the later measurements performed during 2009--2010 which show only a weak correlation along with a gradual increase of the optical flux. We calculate an external seed photon energy density assuming that the gamma-ray emission is due to external Compton scattering. The energy density of the external photons is found to be higher by a factor of two in 2008 compared to 2009--2010. We conclude that the different behaviours observed between the first year and the later years might be explained by postulating two different emission components.

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